1. Field of the Invention
This invention relates in general to ammunition and explosives and, more particularly, to an ignition system for a high intrusion projectile having a granular propellant propulsion system.
2. Description of the Prior Art
The use of flash tubes in the ignition systems of fixed and semifixed gun and cannon ammunition is generally well known. One example of a round having a flash tube in its ignition system is shown in U.S. Pat. No. 2,872,864 to Barnes et al. The patent to Barnes et al. discloses a fin-stabilized round having an elongated hollow boom. The outer wall of the boom is secured by means of a frangible section to a filler plug at the bottom of the cartridge case for the round. The axial bore of the boom is slidably fitted over a metallic center-guide stud which projects forwardly through a bore in the filler plug. The center-guide stud includes an axial flash passage which communicates at its rear end with a primer located at the bottom of the cartridge case and at its front end with the bore of the boom. The bore of the boom in turn communicates with a plurality of transversely drilled holes which communicate with the interior of the cartridge case. In firing the round, the primer is detonated, causing a flame front to travel forwardly through the flash passage in the center-guide stud and outwardly through the transversely drilled holes in the boom to ignite the propellant charge in the cartridge case. The forward force of propulsion is intended to cause the frangible section at the rear of the boom to fracture, allowing the round to travel up the bore of the weapon and out of the cartridge case. At the same time, the center-guide stud offers guidance to the round and prevents the tail fins from bearing against the side walls of the cartridge case.
A serious limitation of the ignition system disclosed by Barnes et al is that the arrangement of the transversely drilled flash holes in the boom does not allow for uniform flame permeation in the bed of propellant in the cartridge case. In addition, the ignition system is expensive, difficult to assemble, and difficult to pack with the propellant charge.
One attempt to overcome the above limitations is described in U.S. Pat. No. 4,572,078 to Bell, which discloses an ignition booster to be used either in place of or in addition to a flash tube. More specifically, the ignition booster consists of a thin film of case-bonded nitrocellulose located on the inside walls and base of the cartridge case. This arrangement allows the booster propellant to be spread out over a greater surface area than is possible within a conventional flash tube. Thus, more uniform permeation of the propellant bed is possible, resulting in enhanced flame spread. However, the round shown by Bell lacks any kind of center-guide or support for increasing the radial stiffness of the round. Thus, the round and its casing are subject to lateral movement during handling and an unacceptable degree of dispersion during firing.
Therefore, a need exists for an improved propellant charge ignition system which enhances flame spread through a granular propellant while also providing projectile boom support.